Piezoelectric relays have in recent years shown promise as alternatives for relays operated electromagnetically. In addition to not requiring windings and cores, such relays offer a number of other advantages among which may be mentioned their low power consumption and heat generation, reduced physical size, relatively simple component parts, and, importantly, their potential for batch fabrication by printed wiring techniques. Further, the voltages required for their operation are sufficiently low to permit integrated circuit control.
Typically, the switch element of a relay operated by piezoelectric or electrostrictive effect comprises a laminate formed of two layers of piezoelectric ceramic material each having an electrode electroplated to each side. The two coated sheets are cemented to opposite sides of a separating conductive centervane, which centervane, in one mode of operation, also constitutes one electrode of the relay. In a well-known fabrication step, the piezoelectric material of each layer has a remanent polarization induced therein by applied direct current electric fields. For the parallel mode of operation contemplated, the layers are polarized in the same direction. In one prior art arrangement, the piezoelectric laminate is mounted at one end on a base member and spaced therefrom by a spacer block. A bracket also mounted on the base member at its other end carries a contact spaced apart from and in alignment with a contact carried at the free end of the laminate. Flexure of the laminate to close the contacts is accomplished in the parallel mode by connecting and grounding the outer electrode coatings of the two layers and applying an operating voltage to the centervane. As a result, electrostatic fields are created in the layers which in one layer agree with the direction of polarization and in the other layer oppose that direction. In accordance with piezoelectric phenomena of ceramic materials, one layer expands lengthwise while the other layer contracts. The resulting stresses cause the laminate to bend; for the cantilever laminate here envisioned, the bending motion is perpendicular to the planes of the laminate electrode coatings thereby causing the contacts to close. Removal of the operating voltage restores the contacts as a result of the restoring mechanical effect.
Although piezoelectric relays have proved themselves in many applications, their fabrication has been attended by a number of problems. Thus, for example, the forces and deflections attainable by piezoelectric effect are relatively small and not uniformly precisely predictable. As a result, the laminate actuator beam (or bimorph as it is frequently termed) must be very accurately positioned relative to the electrical contacts which it controls. This positioning and location of relay parts has in the past been accomplished by the expensive and time-consuming expedient of carefully controlling the dimensions and tolerances of the various relay elements. Even when a maximum adherence to close tolerances is achieved, the difficulty of realizing a piezoelectric laminate of flat, uniform surface contours leaves the problem of inconsistent actuator response from relay to relay upon the application of the same operating voltages. As a result, if the operating gap between the actuator beam and the relay contact spring is maintained of uniform width during fabrication, the control of the spring by the actuator beam may vary from relay to relay and thus affect relay reliability. This invention is thus chiefly directed to the problem of providing a simple and inexpensive method for individually adjusting the operating gap between a contact spring and the actuator beam of a piezoelectric relay without concern for inconsistencies in the mechanical forces generated by the actuator beam.